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[Qemu-devel] Re: [PATCH][RESEND] virtio-serial-bus: Bump up control vq d
From: |
Michael S. Tsirkin |
Subject: |
[Qemu-devel] Re: [PATCH][RESEND] virtio-serial-bus: Bump up control vq descriptors to min. required |
Date: |
Wed, 12 Jan 2011 17:37:58 +0200 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Tue, Jan 11, 2011 at 09:47:44PM +0530, Amit Shah wrote:
> The current default of 16 buffers for the control vq is too small for
> the default max_nr_ports of 32. We can get more entries in there,
> example when asking the guest to add max. allowed ports.
>
> Default to using the minimum required (next power of 2) of the
> max_nr_ports in use.
>
> Signed-off-by: Amit Shah <address@hidden>
> ---
So looking at this more closely, this reduces but does
not eliminate the chance of notification event drops.
I think I liked v1 better.
> hw/virtio-serial-bus.c | 13 ++++++++++---
> 1 files changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/hw/virtio-serial-bus.c b/hw/virtio-serial-bus.c
> index 74ba5ec..eb7b362 100644
> --- a/hw/virtio-serial-bus.c
> +++ b/hw/virtio-serial-bus.c
> @@ -736,7 +736,7 @@ VirtIODevice *virtio_serial_init(DeviceState *dev,
> uint32_t max_nr_ports)
> {
> VirtIOSerial *vser;
> VirtIODevice *vdev;
> - uint32_t i, max_supported_ports;
> + uint32_t i, max_supported_ports, cvq_len;
>
> if (!max_nr_ports)
> return NULL;
> @@ -769,10 +769,17 @@ VirtIODevice *virtio_serial_init(DeviceState *dev,
> uint32_t max_nr_ports)
> /* Add a queue for guest to host transfers for port 0 (backward compat)
> */
> vser->ovqs[0] = virtio_add_queue(vdev, 128, handle_output);
>
> + /*
> + * The number of descriptors to use should always be a power of
> + * two. Use the next power of 2 of max_nr_ports to keep the
> + * entries to a minimum.
> + */
> + cvq_len = 1 << qemu_fls(max_nr_ports - 1);
> +
> /* control queue: host to guest */
> - vser->c_ivq = virtio_add_queue(vdev, 16, control_in);
> + vser->c_ivq = virtio_add_queue(vdev, cvq_len, control_in);
> /* control queue: guest to host */
> - vser->c_ovq = virtio_add_queue(vdev, 16, control_out);
> + vser->c_ovq = virtio_add_queue(vdev, cvq_len, control_out);
>
> for (i = 1; i < vser->bus->max_nr_ports; i++) {
> /* Add a per-port queue for host to guest transfers */
> --
> 1.7.3.4
>